4. Runway Throughput Benefits (May – July)
• Across all wind conditions
– Saving is 78NM per day
– Increase of 20 movements per day
• In strong wind conditions
– Saving is 178NM per day
– Increase of 49 movements per day
Wind
Conditions
Extra Movements
17-hour
scheduled
period
Per Hour
All AWE 20 1.2
Strong AWE
(>20kts)
49 2.9
Wind related ATFM delay reduced by 62%
5. November Results
Estimate over 25,000 minutes of
delay saved in November versus
distance based separation
15 days of strong headwinds
Nov 10th: Zero minutes
ATFM delay with 40 knot
Headwinds
7. Summary of Findings
Reduced cancellations
No Increase in Go Arounds or
Wake Turbulence Encounters
62%
reduction in ATFM
wind delay
178NM
of spacing saved per day
in strong wind conditions (>20kts)
+2.9 movements
per hour in strong wind conditions
83%
of aircraft experienced
smaller Arrival-Arrival
separations
78NM
of spacing on approach
saved per day, on average
+1.2 movements
per hour across all wind conditions
No pilot inquires or comments
In strong headwinds, aircraft fly more slowly over the ground – effectively it is like walking the wrong
way along a moving walkway,
so maintaining a fixed separation distance in accordance with ICAO rules results in a reduced landing
rate.
For example with a Heavy – Heavy wake pair such as a 777 following an A340 the ICAO wake separation
distance is 4nm. In light headwinds it takes the aircraft about 90 seconds to cover this distance.
But with a 35 knot headwind at 3000ft which is not particularly strong, it would take the aircraft 107
seconds to cover the 4 miles, effectively losing 17 seconds worth of runway capacity for that wake pair.
Click Next Block
The new Time Based Separation Rules keep the time interval between arrivals the same irrespective of
headwind conditions and allow us to close up the gap – so in the case of the heavy to heavy wake vortex
pair the gap is reduced to 3.4nm in a 35 knot headwind thereby recovering the lost capacity.
And the data that we have shows that it is safe to do that as the wake vortex decays mush faster in
headwinds. Where wake is an issue is in still air or light quartering tailwinds and under those
circumstances the tools that we have developed will increase separation.
And the benefits are clear – with distance based separation Heathrow’s landing rate in calm winds is
between 40-45 dependent on the mix of arrivals. In strong headwinds this falls to between 32-38
resulting in delays, increased holding and can result in cancellations.
With Time Based Separation we recover more than half of this lost capacity back. The reason why it is not
100% recovery is that we do not drop below minimum radar separation of 3nm.
Went live LOS 24 MAR 2015, CAA Signed off 1 MAY. Won IET Award. Multiple articles written over the past year, been an outstanding success.
Birmingham…
TBS 15 Nov 15, 60 knots headwind at 3000ft (267/60), 4000ft wind 80kts at 270
Arrival Regulation, 36/60
The difference between the target minimum and delivered separation was smaller, suggesting that separations were being delivered consistently closer to the target minimum than in the past.